This invention relates to facsimile transmitters and receivers of the type utilized to transmit and receive information-bearing signals representing the dark/light variations on a document located at the transmitter and converting the information-bearing signals to marks or images on a copy medium located at the receiver so as to form a copy which is a reasonable facsimile of the original document.
Most facsimile transmitters will accommodate documents of various sizes, e.g., various lengths. In facsimile transmitters employing a scanning drum, one edge of the document is typically clamped on the drum, and the drum is rotated while a scanning head moves parallel to the drum in a generally longitudinal direction parallel with the axis of the drum. In such an arrangement, the overall length of the document may vary. However, unless the transmission is somehow interrupted, the transmission will continue until the scanning head has traversed a full length of the drum despite the fact that the document may occupy less than half of the length of the drum. This of course extends the transmission time unnecessarily while the scanning head is scanning the surface of the drum.
It is, of course, possible to terminate the facsimile transmission by merely having the operator stop the transmission once the full length of the document has been scanned. However, operator control cannot, of course, be relied upon in an unattended mode of operation. Moreover, timely operator termination requires that the operator be vigilant during the transmission. Furthermore, termination is subject to operator error which may produce an untimely or early termination of the facsimile transmission resulting in less than all of the information on a document be transmitted. On the other hand, operator termination may be somewhat delayed thereby adding some unnecessary amount of time to the length of the facsimile transmission.
Heretofore, it has been suggested that the duration of a facsimile transmission can be controlled by marking along the margin of a document to be transmitted with a continuous line. The facsimile transmitter then continues to scan the document as long as the line is detected. When the line is no longer detected, the facsimile transmission is terminated. This technique for shortening facsimile transmissions so as to correspond with the length of the document is undesirable in a number of respects. First, the technique requires operator intervention and is therefore subject to operator error. Second, it requires that the document be defaced. Third, the facsimile transmitter must be capable of responding to the line to continue transmission even though the characteristics of that line will vary widely as a function of operator, marking member and the presence of another line on the document. Of course, if the transmitter fails to recognize the line when operating in this particular mode, the transmission may be terminated in an untimely manner.